Phospholipid-and cholestrol-free aqueous composition for topical application to the skin

ABSTRACT

Phospholipid- and cholesterol-free aqueous compositions for topical application to the skin contain a pharmaceutically active ingredient and a vector system of controlled and in-depth transport and release of the active ingredient through the skin. The vector system comprises at least one first non-ionic surfactant which forms vesicles upon dispersion in water and a lamellar phase upon concentrating the vesicles, and at least one second non-ionic hydrophilic surfactant. The ratios of the two non-ionic surfactants are such that the vector system comprises flexible vesicles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/NL95/00325, filed Sep. 27, 1995, basedon EPO 94 202783.0, filed Sep. 27, 1994.

FIELD OF THE INVENTION

The present invention relates to aqueous compositions, containing apharmaceutically active principle and a vector system consisting of amixture of non-ionic surfactants in the form of vesicles having aparticle size between 10 and 1000 nm, for application to the skin.

BACKGROUND OF THE INVENTION

Aqueous compositions containing one or more non-ionic surfactants in theform of vesicles have been known for a long time (see e.g. FR-2315991,published in 1977). From the many scientific articles and patentpublications, which were published since, it will be readily appreciatedby a person of ordinary skill in the art that lipids, and in particularphospholipids and/or cholesterol, and stabilisers, such as sodium laurylsulphate, have to be added to such aqueous compositions containingnon-ionic surfactant(s) in order to prevent coalescence, aggregation,sedimentation and phase transitions, e.g. to a micellar phase.

However, phospholipids and cholesterol appeared to have somedisadvantages when incorporated in compositions, which are intended tobe marketed and, thus, have to meet certain standards. It is known thatphospholipids are not stable on storage at ambient conditions. Specialmeasures are required to protect said compounds against degradation bylight and/or oxygen. Another disadvantage of phospholipids is that--asnaturally occurring products--they are mixtures of ester compounds. Thecomposition of the phospholipids may, thus, vary from batch to batch andfrom source to source. It is also known that cholesterol can be easilyoxidised in the presence of light. Autooxidation may also occur.Although the compound is a naturally occurring compound, also in humanbeings, many efforts are directed to a limitation of the uptake ofexternally administered cholesterol.

Therefore, there is a need to prevent the use of phospholipids andcholesterol in aqueous compositions, comprising one or more non-ionicsurfactants in the form of vesicles and further containing a drug, forapplication to the skin.

SUMMARY OF THE INVENTION

The invention relates to a phospholipid- and cholesterol-free aqueouscomposition for topical application to the skin comprising apharmaceutically active principle and a vector system for the controlledand in-depth transport and release of said active principle through skinlayers, said vector system consisting of at least one first, non-ionicsurfactant, forming vesicles upon dispersion in water and a lamellarphase upon concentrating said vesicles, and at least one second,non-ionic, hydrophilic surfactant, the ratio of said at least one first,non-ionic surfactant and said at least one second, non-ionic surfactantbeing such that the vector system consists of flexible vesicles. Uponlowering the water concentration of the composition a lamellar phase isformed close to a cubic, hexagonal or viscous isotropic phase boundary.

The vesicles of the present invention have a particle size of from 10 to1000 nm.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that aqueous dispersions of vesicles can be made froma mixture of at least two non-ionic surfactants without usingphospholipids and/or cholesterol and derivatives thereof, provided thatat least one of the non-ionic surfactants can intrinsically formvesicles when dispersed in water and a lamellar phase upon concentratingsaid dispersion of vesicles at room temperature. The second surfactantis a hydrophilic surfactant and is not able to intrinsically formvesicles when dispersed in water. The HLB-value for the secondsurfactant is at least 12. In the final composition, comprising amedicament and the said mixture of non-ionic surfactants in water,vesicles are also present and upon lowering the water concentration ofthe composition a lamellar phase is formed which is close to a cubic,hexagonal or viscous isotropic phase boundary, mainly dependent of thenon ionic surfactant(s) used in the mixture.

The non-ionic surfactants, which have appeared to be useful as thelamellar layer forming surfactant on the one hand and as the secondsurfactant on the other hand, are preferably selected from the groupconsisting of polyoxyethylene alkyl ethers and esters (hereafterreferred to as POE-alkyl ethers and esters) sorbitan esters, glucoseesters and sucrose alkyl esters. Examples thereof are listed in thetables below.

                  TABLE I                                                         ______________________________________                                        LAMELLAR LAYER FORMING SURFACTANTS                                            Code/tradename                                                                             Official name  HLB    Supplier                                   ______________________________________                                        L-595        sucrose laurate ester                                                                        5      Ryoto                                                   (30% mono, 70%                                                                di/tri/poly)                                                     Tween ® 81                                                                             POE(5) sorbitan                                                                              10.0   ICI                                                     monooleate                                                       Tween ® 85                                                                             POE(2) sorbitan                                                                              11.0   ICI                                                     trioleate                                                        Span ® 20                                                                              sorbitan mono laurate                                                                        8.6    Sigma                                      Span ® 80                                                                              sorbitan mono oleate                                                                         4.3    ICI                                        Span ® 85                                                                              sorbitan trioleate                                                                           1.8    Sigma                                      Gluc D.O.    dioleyl glucate       Amerchol                                   C.sub.12 EO.sub.3                                                                          POE(3) dodecylether                                                                          9.4    Servo,                                                                        Delden                                     Serdox NOG ®                                                                           POE(4.5) oleylester                                                                          8.7    Servo,                                     S-200                              Delden                                     ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        SECOND SURFACTANT                                                             Code/tradename                                                                             Official name  HLB    Supplier                                   ______________________________________                                        C.sub.12 EO.sub.7                                                                          POE(7) dodecylether                                                                          12.9   Servo,                                                                        Delden                                     Brij ® 96                                                                              POE(10)-oleylether                                                                           12.4   ICI                                        L-1695       Sucrose laurate                                                                              16     Ryoto                                      PEG-8-laurate                                                                              POE(8) dodecylester                                                                          13.5   Diopeg                                     Serdox NOG ®                                                                           POE(10) oleylester                                                                           12.4   Servo,                                     S-440                              Delden                                     ______________________________________                                    

Also mixtures of representatives of these groups may be used.

The mean degree of polymerisation of the POE-alkyl ethers and esters mayrange from 2 to 30 and preferably from 2 to 10. The number of alkylchains is 1 or 2 for the POE- alkyl ethers and esters and-one or morefor the sucrose alkyl esters. The number of carbon atoms in the alkylchain(s) of all non-ionic surfactants belonging to the above-mentionedgroup may range from 8 to 30 and preferably from 12 to 17. The alkylchain(s) may be straight or branched, saturated or unsaturated. In caseof a saturated alkyl chain there is a preference for 1-dodecyl (lauryl).In case of an unsaturated alkyl chain there is a preference for oleyl.

The total concentration of non-ionic surfactants may be up to 15 wt %,the percentage being based on the weight of the composition. However, itis preferred to use concentrations up to 7.5 wt % and more preferably upto 5 wt %.

The particle size of the vesicles may range from 10 to 1000 nm, but forparticle sizes ranging from 50 to 500 nm are preferred. A particle sizefrom 100 to about 250 nm however is most preferred. By extruding thedispersion of vesicles through a membrane, having a pore size of≦1/3*vesicle diameter, the mean particle size of the vesicles in general isnot changed.

In view of the stability of the vesicles it is important that afterextrusion the dispersion still be homogeneous, a measure for thehomogeneity being the polydispersity index as measured by means of adynamic light scattering apparatus.

The ratio of the non-ionic surfactant(s), intrinsically forming vesicleswhen dispersed in water, to the non-ionic surfactant(s), not formingvesicles in water, may vary according to the surfactants and the drugused. However, it should be stressed that it is important that the finalcomposition still contain vesicles, because of the possibilities forencapsulating a drug into the vesicles.

To the compositions according to the present invention an ionicsurfactant as a stabiliser may occasionally be added. Examples thereofare sodium laurate and sodium dicetyl phosphate.

The present vesicles may also contain a fatty alcohol, specifically aC₁₅ -C₂₅ fatty alcohol, preferably a C₂₀ -C₂₄ fatty alcohol. Since thesaid compounds are well-known as thickening agents and/or asco-emulsifiers in the preparation of solid and semi-solid fattycompositions such as sticks, creams and ointments, it is surprising thatthe addition of the fatty alcohols to the vesicles of the presentinvention, does not have a negative impact on the extrudability and meanparticle size as compared with those of the vesicles not containing afatty alcohol.

The drug in the compositions according to the present invention may beencapsulated in the vesicles, may adhere to the vesicles or may belocated in the aqueous continuous phase. It will be readily understoodthat there is an upper limit to the amount of drug that can beencapsulated into the vesicles and that the ratio of encapsulated drugto not-encapsulated drug depends on the concentration and composition ofthe vesicles and the properties of the drug.

The aqueous compositions containing a mixture of non-ionic surfactantsin the form of vesicles can be prepared according to methods as known inthe art of liposome and niosome technology.

The compositions according to the present invention are applied to theskin in order to deliver the medicament incorporated therein to theplace where the therapeutical action is required or can becomeeffective. Advantageously the compositions of the present invention canbe used for intradermal as well as for transdermal administration ofdrugs.

Biodistribution studies performed with several dispersions of vesiclesaccording to the present invention and a prior art compositioncontaining rigid vesicles (composition III in Example 9) clearlydemonstrate that the dispersions containing flexible vesicles penetrateinto the skin faster, deeper and to a greater extent than the prior artdispersion (see also FIG. 1, tables III-VI).

The composition containing a fatty alcohol (composition IV) in additionthereto penetrates into the skin faster, deeper and to a greater extentthan the corresponding composition not containing such a fatty alcohol(composition I, tables III-VI, FIG. 1).

From FIG. 2 it clearly appears that the ¹⁴ C-label apparently penetratesinto the skin at a lower rate than the ³ H-label (see also tables III toVII).

The compositions according to the present invention offer interestingpossibilities for pharmaceutical product development.

Vesicles can be prepared without being forced to use phospholipidsand/or cholesterol which have appeared to be broken down on storage andadversely affect the stability of the vesicles.

In the second place there is only a limited amount of non-ionicsurfactants that have the intrinsic property of forming vesicles whendispersed in water and a lamellar phase upon concentrating saidvesicles. By mixing a non-ionic surfactant which is able to do so withone or more non-ionic surfactants, which intrinsically do not formvesicles when dispersed in water and a lamellar phase upon lowering thewater concentration but a cubic, hexagonal or viscous isotropic phase ondispersion in water, the scope of surfactants that can be used inproduct development is widely broadened.

Furthermore, by using a mixture of non-ionic surfactants and varying theratio of the components, the properties of the vesicles can be changedin order to comply with the standards set for the final product, e.g.with respect to the amount of encapsulated drug, rate of release of thedrug from the vesicles.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity andunderstanding, it will be readily apparent to those of ordinary skill inthe art in the light of the teachings of this invention that certainchanges and modifications may be made thereto without departing from thespirit and the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following examples and accompanying figures illustrate theinvention.

FIG. 1 shows the distribution of radio-activity recovered from the skin,6 h after dermal application of several formulations,

FIG. 2 shows the percentage radio-activity in deep skin afterapplication of formulation IV,

FIG. 3 shows the ratio deep skin/upper skin recovered at 6,24 and 48 hafter dermal application of several formulations.

EXAMPLES Example 1

A mixture of non-ionic surfactants (see the tables for the composition;the weight ratio of the surfactants used is based on their molecularweights) in an amount required to obtain a final aqueous dispersioncontaining 5 wt % was dissolved in about 2 ml of a mixture ofchloroform/ methanol (3/1) in a test tube. The mixture of organicsolvents was subsequently evaporated by means of overnight vacuumcentrifugation. The remaining dry film in the test tube was hydrated byadding 5 ml of Phosphate Buffered Saline (PBS; pH of 7.4). The tube wasplaced in a water bath of 8° C. for 10 minutes. Thereafter thedispersion was sonicated at 80° C. for 45 seconds. After cooling thedispersion to room temperature, the same was extruded using an extruder(Sartorius), equipped with an extrusion membrane (pore size 200 nm;Nuclepore) and operated under nitrogen pressure of about 1-1.5 bar. Bymeans of polarised light microscopy and dynamic light scattering thepresence of vesicles was assessed and the mean particle size thereofdetermined.

    ______________________________________                                        Mixtures of POE(3)-dodecyl ether (=C.sub.12 EO.sub.3) and POE(7)-dodecyl      ether (=C.sub.12 EO.sub.7)                                                                  stable dispersion                                                                           mean particle size                                ratio C.sub.12 EO.sub.3 :C.sub.12 EO.sub.7                                                  of vesicles   of vesicles (nm)                                  ______________________________________                                        0.9:0.1       yes           166, 167                                          0.8:0.2       yes           157                                               0.7:0.3       yes           151, 126                                          0.6:0.4       yes           177, 184                                          0.5:0.5       yes           164, 149, 182                                     0.4:0.6       yes           167, 186                                          0.3:0.7       yes           101, 189                                          ______________________________________                                    

    ______________________________________                                        Mixtures of sucrose laurate ester (Ryoto L-595) and POE(7)-                   dodecyl ether (=C.sub.12 EO.sub.7)                                            ratio Ryoto L-595:                                                                         stable dispersion                                                                            mean particle size                                C.sub.12 EO.sub.7                                                                          of vesicles    of vesicles (nm)                                  ______________________________________                                        0.3:0.7      yes            132, 142, 138, 138                                0.2:0.8      yes            139, 130, 135,                                                                142, 132, 143                                     0.1:0.9      yes            110, 141, 84                                      ______________________________________                                    

    ______________________________________                                        Mixtures of POE(4.5)-oleyl ester (=S-200) and POE(10)-oleyl                   ester (=S-440)                                                                            stable dispersion                                                                            mean particle size                                 ratio S-200:S-440                                                                         of vesicles    of vesicles (nm)                                   ______________________________________                                        0.6:0.4     yes            288                                                0.5:0.5     yes            223                                                0.4:0.6     yes            183                                                0.3:0.7     yes            155, 155                                           0.2:0.8     yes            144, 136, 135                                      0.1:0.9     yes            120, 114                                           ______________________________________                                    

Example 2

The experiments as described under Example 1 were repeated, but thevesicles-containing dispersions, after extrusion through a 200 nm poresize membrane were additionally extruded using the same extruder(Sartorius), equipped with an extrusion membrane (pore size 30 nm;Nuclepore) and operated under nitrogen pressure of about 4 bar. The meanparticle size of the vesicles and polydispersity index after extrusionthrough the first membrane and through the second membrane weredetermined, by dynamic light scattering (DLS) at 25° C. with a Malvern4700 system using a 25 mW He--Ne laser (NEC, Tokyo, Japan) and theautomeasure version 3.2 software (Malvern Ltd., Malvern, UK). Forviscosity and refractive index values of the water were used. The systemreports a polydispersity index as a measure of the particle sizedistribution. This index ranges from 0.0 for an entirely homogeneousdispersion up to 1.0 for a dispersion with a completely heterogeneoussize distribution.

    ______________________________________                                        Mixtures of POE(3)-dodecyl ether (=C.sub.12 EO.sub.3) and POE(7)-dodecyl      ether (=C.sub.12 EO.sub.7)                                                             mean particle size (nm) of vesicles after                                     extrusion through: (polydispersity index                                      between brackets)                                                    ratio      200 nm pore size mem-                                                                        30 nm pore size mem-                                C.sub.12 EO.sub.3 :C.sub.12 EO.sub.7                                                     brane          brane                                               ______________________________________                                        0.9:0.1    139(0.19), 153(0.13)                                                                         139(0.32), 156(0.31)                                0.8:0.2    145(0.13), 148(0.16)                                                                          97(0.25), 78(0.22)                                 0.7:0.3    136(0.19), 126(0.19)                                                                         110(0.34) 77.3(0.22)                                0.6:0.4    184(0.15), 165(0.11),                                                                        204(0.21), 185(0.14),                                          204(0.15)      188(0.21)                                           0.5:0.5    198(0.13), 182(0.15),                                                                        168(0.15), 176(0.16),                                          172(0.13), 192(0.14)                                                                         183(0.14), 186(0.15)                                0.4:0.6    167(0.15), 186(0.15),                                                                        172(0.11), 176(0.19),                                          165(0.15), 193(0.15)                                                                         251(0.38), 190(0.20)                                0.3:0.7    189(0.25)      128(0.30)                                           ______________________________________                                    

    ______________________________________                                        Mixtures of sucrose laurate ester (Ryoto L-595) and POE(7)-                   dodecyl ether (=C.sub.12 EO.sub.7)                                                    mean particle size (nm) of vesicles after                                     extrusion through: (polydispersity index                                      between brackets)                                                     ratio Ryoto                                                                             200 nm pore size mem-                                                                         30 nm pore size mem-                                L-595:C.sub.12 EO.sub.7                                                                 brane           brane                                               ______________________________________                                        0.3:0.7   142(0.10), 138(0.09),                                                                         119(0.11), 137(0.07),                                         138(0.14)       121(0.10)                                           0.2:0.8   151(0.12), 138(0.12),                                                                         161(0.19), 157(0.17),                                         142(0.07), 132(0.11),                                                                         134(0.15), 147(0.21),                                         143(0.12)       132(0.18)                                           0.1:0.9    83.5(0.36)     141(0.30)                                           ______________________________________                                    

    ______________________________________                                        Mixtures of POE(4.5)-oleyl ester (=S-200) and POE(10)-oleyl                   ester (=S-440)                                                                         mean particle size (nm) of vesicles after                                     extrusion through: (polydispersity index                                      between brackets)                                                    ratio S-200:                                                                             200 nm pore size                                                                             30 nm pore size mem-                                S-440      membrane       brane                                               ______________________________________                                        0.3:0.7    155(0.24), 155(0.25)                                                                         88.1(0.21), 86.3(0.20)                              0.2:0.8    136(0.25), 135(0.25)                                                                         76.0(0.19), 75.1(0.20)                              0.1:0.9    120(0.23), 114(0.23)                                                                         68.8(0.19), 68.0(0.16)                              ______________________________________                                    

Example 3

Experiments were performed as described under example 2 using C₁₂ EO₇ asthe second surfactant. The dispersion after extruding through the firstmembrane (200 nm pore size) was extruded through a second membranehaving a pore size of either 30 nm or 50 nm. The extrusion rate(mg/min.) is determined by dividing the amount of dispersion ofvesicles, extruded through the extruding membrane for a period of 3 to10 min. after the first droplets were extruded, by the said period. Thetotal amount of dispersion extruded is about 1 to 1,5 ml.

    ______________________________________                                        C.sub.12 EO.sub.7                                                                     L-595         Vesicles                                                                              extrudability                                   ______________________________________                                        4       6             +/-     +/-                                             3       7             +       +                                               2       8             +       +                                               ______________________________________                                                Tween ®                                                           C.sub.12 EO.sub.7                                                                     81            Vesicles                                                                              extrudability                                   ______________________________________                                        6       4             +/-     +                                               4       6             +       +                                               2       8             +       +                                               1       9             +/-     +                                               0.5     9.5           +/-     +                                               ______________________________________                                                Tween ®                                                           C.sub.12 EO.sub.7                                                                     85            Vesicles                                                                              extrudability                                   ______________________________________                                        4       6             +       +                                               2       8             +       +                                               0       10            +       +                                               ______________________________________                                                Span ®                                                            C.sub.12 EO.sub.7                                                                     20            Vesicles                                                                              extrudability                                   ______________________________________                                        6       4             +/-     +                                               ______________________________________                                                Span ®                                                            C.sub.12 EO.sub.7                                                                     80            Vesicles                                                                              extrudability                                   ______________________________________                                        6       4             +/-     +                                               4       6             +/-     +                                               ______________________________________                                                Gluc                                                                  C.sub.12 EO.sub.7                                                                     D.O.          Vesicles                                                                              extrudability                                   ______________________________________                                        6       4             +/-     +                                               4       6             +/-     +                                               ______________________________________                                         Vesicles                                                                      + : vesicles present; +/- : vesicles and spheres                              Extrudability                                                                 + : extrusion through 30 nm pore size membrane or extrusion through 50 nm     pore size membrane (>1000 mg/min)                                             +/- : extrusion through 50 nm pore size (100-1000 mg/min)                

Example 4

Experiments were performed as described under example 2 using Brij® 96as the second surfactant. The dispersion after extruding through thefirst membrane (200 nm pore size) was extruded through a second membranehaving a pore size of either 30 nm or 50 nm.

    ______________________________________                                        Brij ®                                                                             Tween ®                                                          96       85           Vesicles                                                                              extrudability                                   ______________________________________                                        6        4            +/-     +                                               4        6            +       +                                               2        8            +       +                                               0        10           +       +                                               ______________________________________                                        Brij ®                                                                             Span ®                                                           96       20           Vesicles                                                                              extrudability                                   ______________________________________                                        4        6            +/-     +                                               ______________________________________                                        Brij ®                                                                             Span ®                                                           96       85           Vesicles                                                                              extrudability                                   ______________________________________                                        4        6            +/-     +/-                                             ______________________________________                                         For the meaning of the symbols see example 3                             

Example 5

Experiments were performed as described under example 2 using. L-1695 asthe second surfactant. The dispersion after extruding through the firstmembrane (200 nm pore size) was extruded through a second membranehaving a pore size of either 30 nm or 50 nm.

    ______________________________________                                        L-1695   L-595        Vesicles                                                                              extrudability                                   ______________________________________                                        6        4            +       +                                               4        6            +       +                                               2        8            +       +                                               3        7            +       +                                               ______________________________________                                                 PEG-8                                                                         lau-                                                                 L-595    rate         Vesicles                                                                              extrudability                                   ______________________________________                                        7        3            +       +                                               9        1            +       +/-                                             ______________________________________                                         For the meaning of the symbols see example 3                             

Example 6

A dispersion of vesicles was prepared using L-595 as the lamellar layerforming surfactant, L-1695 as the second surfactant and dicetylphosphate as a stabiliser in a molecular weight ratio of5.875:3.875:0.25. The dispersion of vesicles could be extruded through a30 nm pore size membrane.

Example 7

Tween® 81 and L-595 (lamellar layer forming surfactants) and C₁₂ EO₇(second surfactant) in a molecular weight ratio of 9.5:2:0.5 weredispersed in water. Both vesicles and spheres could be observed by meansof a polarised light microscope. The dispersion could be extrudedthrough a 30 nm pore size membrane.

Example 8

The manufacturing method of example 1 was followed, but now 2.5% of1-docosanol was added to the solution of surfactants in the mixture ofchloroform/methanol. The combinations of non-ionic surfactants usedwere:

1. C₁₂ EO₇ : L-595 (3:7)

2. L-1695: L-595 (4:6)

3. PEG(8) laurate: L-595 (7:3).

4. Also 1-docosanol was incorporated in vesicles consisting of L-1695,L-595 and dicetyl phosphate in a molecular weight ratio of 3:7:0.1.

The dispersions of vesicles nos 1 and 3 containing 1-docosanol had thesame characteristics as the vesicles without containing 1-docosanol.Incorporating 1-docosanol in the composition no. 2 had a negativeimpact. By the addition of the stabiliser dicetyl phosphate (compositionno. 4) a dispersion of vesicles could be obtained, the vesicles having adiameter slightly greater than those without containing 1-docosanol.

Example 9 Biodistribution Studies of Topically Applied CompositionsAccording to the Present Invention

Materials

Non-ionic surfactants were obtained from the companies as specified inthe tables I and II. Cholesterol and dicetyl phosphate were supplied bySigma Chemicals (St. Louis, Mo., USA). 1α, 2α(n)-³ H!cholesteryl oleoylether (spec. act. 1.71 TBq/mmol) was supplied by Amersham(Buckinghamshire, UK). Hionic Fluor, Plasmasol and Soluene-350 werepurchased from Packard Instruments (Downers Grove, Ill., USA). All otherreagents were of analytical grade.

Preparation of ³ H!-Labelled Vesicles

Vesicles were composed of a mixture of several non-ionic surfactants. ³H!-cholesteryl oleoyl ether was added as a radioactive marker. Ingeneral, 25 mg of non-ionic surfactants and ³ H!-cholesteryl oleoylether were dissolved in a mixture of chloroform/ methanol (3:1) v/v) andevaporated to dryness under N₂ for at least 90 min. The film washydrated in 500 μl sterile PBS (3.6 mM KH₂ PO₄, 6.4 mM NaH₂ PO₄, 145 mMNaCl, pH 7.4) or in a sterile phosphate buffered glucose solution. Theresulting dispersion was subsequently sonicated preferably until a meanparticle size between 100 and 150 nm was obtained.

Preparation of ³ H!- and ¹⁴ C!-Labelled Vesicles

Vesicles were prepared of a mixture of L-595 and C₁₂ EO₇ as describedunder previous paragraph, but now docosanol and ¹⁴ C!-labelled docosanolwere added in such an amount that the vesicles contained about 7*10³mol. % ³ H!-cholesteryl oleoylether and a mixture of docosanol and .sup.11 C!-labelled docosanol (composition IV, table III).

Animals

Wistar rats (U:WU,CPB) with an average weight of 240-260 g from theanimal facility of the University of Utrecht were used. Animals receivedstandard laboratory chow and water ad libitum.

Animal Experiments

Prior to application of vesicles, rats were injected i.p. with a mixtureof ketamine, xylazine and atropine (KRA). Subsequently, hair of thelower part of the neck/upper part of the back was clipped. 24 hoursafter clipping of the hair, ³ H!-labelled vesicles were applied to 1 cm²of clipped skin of rats under KRA anaesthesia. The amount of surfactantper application was 1 mg in a volume of 20 μl.

At 6, 24, 48 and occasionally 96 hours post-application rats wereanaesthetised with ether. Rats were then killed by cervical dislocation.Subsequently the site of application as well as surrounding tissue waswiped twice with a water wetted swab and once with a dry swab. Then thesite of application was stripped 20 times with tape. Finally, remainingskin was excised and radioactivity in swabs, each strip and skin wasdetermined.

Radioactivity Measurements

Radioactivity in swabs and strips was determined by adding 10 ml ofHionic and warming the samples overnight at 40° C.

Radioactivity in remaining skin at the site of application wasdetermined by dissolving the skin completely in respectively 7, 3 and 1ml of Soluene-350. To 750 μl of dissolved skin 10 ml of Hionic wasadded. Radioactivity was assayed with 10 ml of Hionic as a scintillationfluid.

The results of the above tests are given in tables IV to VII and FIGS.1, 2 and 3.

TABLE III-VII

                                      TABLE III                                   __________________________________________________________________________    Vesicles-containing preparations as used in the biodistribution studies       composition.sup.1                                                                           dose   size (nm)                                                                          pd remarks                                          __________________________________________________________________________    I  L595:C.sub.12 E0.sub.7                                                                   1 mg = 20 μl                                                                      119  0.33                                                   (7:3)                                                                      II L595:PEG8-laurate                                                                        1 mg = 20 μ1                                                                      119  0.31                                                   (7:3)                                                                      III                                                                              WASAG7:Chol:DCP                                                                          1 mg = 20 μl                                                                      109  0.35                                                   (5:4:1)                                                                    IV L595:C.sub.12 E0.sub.7 :docosanol.sup.2                                                  1 mg = 20 μl                                                                      126  0.33                                                   (7:3:0.1)                                                                  V  L595:L1695:DCP                                                                           1 mg = 20 μl                                                                      196  0.14                                                                             a phosphate buffered glucose solution was           (7:3:0.1)                 chosen as hydration medium                       VI C.sub.12 E0.sub.7 :Tween ® 81                                                        1 mg = 20 μl                                                                      158  0.19                                                                             a phosphate buffered glucose solution was           (1:9)                     chosen as hydration medium                       __________________________________________________________________________     .sup.1 vesicles contained about 1*10.sup.3 mol %  .sup.3                      Hcholesteryloleoylether                                                       .sup.2 vesicles contained about 7*10.sup.3 mol %  .sup.3                      Hcholesteryloleoylether and a mixture of docosanol and .sup.14 Clabeled       docosanol                                                                

                                      TABLE IV                                    __________________________________________________________________________    Biodistribution as percentage of dose radioactivity 6 h after                 application                                                                   vesicles.sup.1                                                                             label                                                                              swabs                                                                              strips                                                                             deep skin.sup.2                                                                     total.sup.3                                 __________________________________________________________________________    I  L595:C.sub.12 E0.sub.7                                                                  .sup.3 H                                                                           67 (±4)                                                                         25 (±5)                                                                         5.9 (±1.5)                                                                       98 (±2)                                  II L595:PEG8-laurate                                                                       .sup.3 H                                                                           61 (±3)                                                                         23 (±3)                                                                         10 (±0.1)                                                                        93 (±3)                                  III                                                                              WASAG7:Chol:                                                                            .sup.3 H                                                                           86 (±3)                                                                         14 (±2)                                                                         1.4 (±0.4)                                                                       101 (±0.2)                                  DCP                                                                        IV L595:C.sub.12 E0.sub.7 :                                                                .sup.3 H                                                                           61 (±4)                                                                         24 (±5)                                                                         9.3 (±1.1)                                                                       95 (±2)                                     docosanol                                                                               .sup.14 C                                                                          85 (±4)                                                                         16 (±2)                                                                         3.7 (±0.5)                                                                       105 (±4)                                              ratio.sup.4                                                                        0.72 1.45 2.51  0.90                                                     .sup.3 H/.sup.14 C                                                                 (±0.03)                                                                         (±0.21)                                                                         (±0.46)                                                                          (±0.02)                                  V  L595:L1695:DCP                                                                          .sup.3 H                                                                           71 (±2)                                                                         26 (±2)                                                                         3.0 (±0.7)                                                                       100 (±l)                                 VI C.sub.12 E0.sub.7 :Tween ® 81                                                       .sup.3 H                                                                           62 (±2)                                                                         15 (±3)                                                                         7.5 (±1.1)                                                                       85 (±3)                                  __________________________________________________________________________     .sup.1 for detailed description see table III                                 .sup.2 remaining skin at site of application after swabs and strips           .sup.3 total amount recovered from strips, swabs and remaining skin           .sup.4 ratio .sup.3 H/.sup.14 C calculated as percentage of dose .sup.3 H     divided by percentage of dose .sup.14 C recovered                        

                                      TABLE V                                     __________________________________________________________________________    Biodistribution as percentage of dose radioactivity 24 h after                application                                                                   vesicles.sup.1                                                                             label                                                                              swabs                                                                              strips                                                                             deep skin.sup.2                                                                     total.sup.3                                 __________________________________________________________________________    I  L595:C.sub.12 E0.sub.7                                                                  .sup.3 H                                                                           40 (±7)                                                                         22 (±4)                                                                         12 (±1)                                                                          73 (±11)                                 II L595:PEG8-laurate                                                                       .sup.3 H                                                                           45 (±2)                                                                         17 (±3)                                                                         18 (±3)                                                                          80 (±2)                                  III                                                                              WASAG7:Chol:                                                                            .sup.3 H                                                                           45 (±15)                                                                        18 (±2)                                                                         5 (±1)                                                                           67 (±14)                                    DCP                                                                        IV L595:C.sub.12 E0.sub.7 :                                                                .sup.3 H                                                                           51 (±4)                                                                         19 (±3)                                                                         18 (±1)                                                                          88 (±4)                                     docosanol                                                                               .sup.14 C                                                                          66 (±7)                                                                         19 (±1)                                                                         11 (±2)                                                                          97 (±4)                                               ratio.sup.4                                                                        0.77 1.04 1.58  0.91                                                     .sup.3 H/.sup.14 C                                                                 (±0.06)                                                                         (±0.23)                                                                         (±0.25)                                                                          (±0.01)                                  V  L595:L1695:DCP                                                                          .sup.3 H                                                                           52 (±4)                                                                         27 (±2)                                                                         13 (±4)                                                                          93 (±0.5)                                VI C.sub.12 E0.sub.7 :Tween ® 81                                                       .sup.3 H                                                                           32 (±5)                                                                         15 (±0.4)                                                                       17 (±2)                                                                          64 (±4)                                  __________________________________________________________________________     .sup.1 for detailed description see table III                                 .sup.2 remaining skin at site of application after swabs and strips           .sup.3 total amount recovered from strips, swabs and remaining skin           .sup.4 ratio .sup.3 H/.sup.14 C calculated as percentage of dose .sup.3 H     divided by percentage of dose .sup.14 C recovered                        

                  TABLE VI                                                        ______________________________________                                        Biodistribution as percentage of dose radioactivity 48 h after                application                                                                   vesicles.sup.1   label    strips   deep skin.sup.2                            ______________________________________                                        I    L595:C.sub.12 E0.sub.7                                                                        .sup.3 H 19 (±3)                                                                           14 (±2)                               II   L595:PEG8-laurate                                                                             .sup.3 H 15 (±3)                                                                           16 (±2)                               III  WASAG7:Chol:DCP .sup.3 H 15 (±2)                                                                           4.1 (±1.2)                            IV   L595:C.sub.12 E0.sub.7 :docosanol                                                             .sup.3 H 19 (±3)                                                                           22 (±2)                                                    .sup.14 C                                                                              22 (±1.4)                                                                         17 (±2)                                                    ratio.sup.3                                                                            0.87   1.32                                                          .sup.3 H/.sup.14 C                                                                     (±0.06)                                                                           (±0.11)                               V    L595:L1695:DCP  .sup.3 H 20 (±1)                                                                           12 (±3)                               VI   C.sub.12 E0.sub.7 :Tween ® 81                                                             .sup.3 H 18 (±2)                                                                           12 (±1)                               ______________________________________                                         .sup.1 for detailed description see table III                                 .sup.2 remaining skin at site of application after swabs and strips           .sup.3 ratio .sup.3 H/.sup.14 C calculated as percentage of dose .sup.3 H     divided by percentage of dose .sup.14 C recovered                        

                  TABLE VII                                                       ______________________________________                                        Biodistribution as percentage of dose radioactivity 96 h after                application                                                                   vesicles.sup.1   label    strips   deep skin.sup.2                            ______________________________________                                        L595:C.sub.12 E0.sub.7 :docosanol                                                              .sup.3 H 21 (±5)                                                                             9.0 (±2.1)                                               .sup.14 C                                                                              23 (±4)                                                                             14 (±3)                                                  ratio.sup.3                                                                            0.91     0.65                                                        .sup.3 H/.sup.14 C                                                                     (±0.15)                                                                             (±0.03)                                 ______________________________________                                         .sup.1 for detailed description see table III                                 .sup.2 remaining skin at site of application after swabs and strips           .sup.3 ratio .sup.3 H/.sup.14 C calculated as percentage of dose .sup.3 H     divided by percentage of dose .sup.14 C recovered                        

I claim:
 1. Phospholipid- and cholesterol-free aqueous composition fortopical application to the skin comprising a pharmaceutically activeprinciple and a vector system for the controlled and in-depth transportand release of said active principle through skin layers, said vectorsystem consisting of at least one first, non-ionic surfactant, saidfirst non-ionic surfactant forming vesicles upon dispersion in water anda lamellar phase upon concentrating said vesicles, and at least onesecond, non-ionic, hydrophilic surfactant which does not intrinsicallyform vesicles when dispersed in water, the ratio of said at least onefirst, non-ionic surfactant and said at least one second, non-ionicsurfactant being such that the vector system consists of flexiblevesicles.
 2. Aqueous composition according to claim 1, wherein uponlowering the water concentration of the composition a lamellar phase isformed close to a cubic, hexagonal or isotropic phase boundary. 3.Aqueous composition according to claim 1, wherein said vesicles have aparticle size of from 10 to 1000 nm.
 4. Aqueous composition according toclaim 3 wherein said vesicles have a particle size of from 50 to 500 nm.5. Aqueous composition according to one claim 1, wherein said flexiblevesicles can be extruded through an extrusion membrane having pore sizesof about 20 to 70 nm.
 6. Aqueous composition according to claim 5wherein said flexible vesicles can be extruded through an extrusionmembrane having pore sizes of about 30 to 50 nm.
 7. Aqueous compositionaccording to claim 1, wherein said second surfactant has an HLB value ofat least
 12. 8. Aqueous composition according to claim 1, wherein saidnon-ionic surfactants are selected from the group consisting ofpolyoxyethylene ethers, polyoxyethylene esters, sucrose esters, sorbitanesters and glucate esters.
 9. Aqueous composition according to claim 1,wherein said first, non-ionic surfactant is selected from the groupconsisting of:sucrose laurate ester (30% mono, 70% di/tri/poly), POE(5)sorbitan monooleate, POE(2) sorbitan trioleate, sorbitan monolaurate,sorbitan monooleate, sorbitan trioleate, dioleyl glucate, POE(3) dodecylether and POE(4,5) oleylester.
 10. Aqueous composition according toclaim 9, wherein said first non-ionic surfactant is selected from thegroup consisting of POE(3)-dodecyl ether, sucrose laurate ester,POE(5)-sorbitan mono-oleate, and POE(2)-sorbitan tri-oleate.
 11. Aqueouscomposition according to claim 1, wherein said second non-ionicsurfactant is selected from the group consisting of:POE(7) dodecylether, POE(10) oleylether, POE(8) dodecylester, POE(10) oleylester andsucrose laurate.
 12. Aqueous composition according to claim 11, whereinsaid second non-ionic surfactant is selected from the group consistingof POE(7)-dodecylether, sucrose laurate ester and POE(8)-dodecyl ester.13. Aqueous composition according to claim 1, wherein said compositionfurther comprises a stabiliser.
 14. Aqueous composition according toclaim 1, wherein the concentration of non-ionic surfactants amounts upto 15 wt % based on the weight of the composition.
 15. Aqueouscomposition according claim 1, wherein said composition furthercomprises a C₁₅ -C₂₅ fatty alcohol.
 16. Aqueous composition according toclaim 15, wherein said composition further comprises a C₂₀₋₂₄ fattyalcohol.
 17. A composition for topical application to the skincomprising an effective amount of a medication that can be administeredby intradermal and/or transdermal delivery to a patient in need thereinand an aqueous composition according to claim 1.